The present invention relates to hydraulic turning devices for a turn plow connectable to a tractor. The turning device mainly comprises a substantially upright double-acting cylinder having a piston dividing the cylinder into an upper and a lower compartment, and the piston is operatively connected to the turn plow for turning the latter in two steps between a first and a second through 180.degree. reversed position. The upper and the lower cylinder compartments are connected by fluid passage with a control device having a fluid inlet passage and a fluid return passage, and which is provided for reversing the movement of the piston in the cylinder with a valve having an axially movable valve spool, a reversing piston and a reversing valve. The valve spool controls filling of the lower cylinder compartment and also controls a pressure valve located between the upper cylinder compartment and the fluid return passage. The reversing piston is arranged in a fluid passage provided with a one-way valve, and extending between the inlet passage and the upper cylinder compartment and controls filling of the latter with pressure fluid, whereas the reversing valve controls, dependent on the pressure acting thereon, movement of the reversing piston. In a known construction of the aforementioned kind it is necessary that the two cylinder compartments of the hydraulic cylinder are connected with each other by a passage through the piston in which a one-way valve is arranged, whereby this passage, in the moment of the reversing of the piston movement, has to be closed by an additional closure means. Such a passage through the piston, the mounting of a one-way valve in the passage, and the additional arrangement of closure means complicate manufacture of the arrangement and require very close tolerances in order to assure trouble free function thereof. In this known construction, the control device forms the cover, respectively the bottom of the hydraulic cylinder and is welded to one end of the latter, and a flange is welded to the control device for tiltably mounting the hydraulic cylinder. In this arrangement is is necessary that the housing of the control device is formed from weldable material and this arrangement has the additional disadvantage that, during welding, the exact bores in the control device are subjected to distortion and usually have to be refinished.